Quinacridone pigment, known as an organic pigment, is a high weather resistant pigment showing a wide range of hues from violet to orange-yellow with red in the center, and has been widely used as a colorant in the range where gravure and flexo inks, colorants for plastics, paints, lithographic inks, toners, ink-jet inks and the like are available. From the practical aspect, severe requirements have been imposed thereto in terms of fastness characteristic and tint characteristic.
Among primary aromatic amines, there is a carcinogenetic kind, and its influence on the human body has recently been reported. Regulation of PAA in organic pigments used for various applications as a coloring material has been started in many countries. The regulation value thereof has conventionally been “less than 500 ppm”, in accordance with AP(89)1 (EU Resolution on the Use of Colourants in Plastic Materials Coming into Contact with Food), BfR (the Federal Institute for Risk Assessment in Germany) Recommendation IX (Regulation for Colorants for Plastics and Other Polymers Used in Commodities), a self-imposed regulation by the Japan Hygienic Olefin and Styrene Plastics Association, and the like. However, carcinogenic o-anisidine was detected by a measurement method of PAA in paper napkin (EN645) established in 2008, and this triggered a movement to legislate PAA in paper napkin to 10 ppb or less (targeting the ultimate value of 0) in LUA (Landesuntersuchungsamt: a state laboratory in Germany). This value corresponds to a very severe value of 10 ppm or less in a pigment, and hence we pigment manufacturers have to promptly address the problem.
PTL 1 proposes a disazo pigment and a method for producing the disazo pigment, characterized by comprising, coupling a tetrazo solution of a benzidine compound with a coupler solution containing an acetoacetanilide compound to obtain a disazo pigment slurry, and treating the pigment slurry by adding a hypoiodite salt to the slurry and then precipitating fine particles of iodine under an acidic condition.
PTL 2 proposes a method for producing a disazo pigment with a low amine content, characterized by comprising, coupling a tetrazo solution of a benzidine compound with a coupler solution containing an acetoacetanilide compound in a stoichiometrically excess amount relative to the benzidine compound to obtain a disazo pigment slurry, and adding a halogen to the slurry, thereby treating the excess amount of the acetoacetanilide compound, and a disazo pigment obtained by the method.
PTL 3 proposes a method for producing a disazo pigment, characterized by comprising, coupling a tetrazo solution of a benzidine compound with a coupler solution containing an acetoacetanilide compound in a stoichiometrically excess amount relative to the benzidine compound to obtain a disazo pigment slurry, and adding an oxidizing agent to the slurry, thereby oxidatively decomposing the excess amount of the acetanilide compound.